It is very common for Chiropractors to assess the sacroiliac joint on every patient, but have you ever really analysed this incredible joint and its implications to the function of the entire body? This is the first in a 3-part article - the next 2 parts will be available on our website www.soto.nz in Dec and Jan. The sacroiliac joint is a crucial part of SOT protocols and understanding the different presentations could significantly enhance your confidence and results in practice.
This month will introduce the SI joint anatomy, mobility and stability in detail. We look at the ‘normal’ joint and introduce the more complicated and challenging C-shape SI joint.
Part 2 looks at the Straight and Tubercle SI joint morphologies including clinical and rehab considerations, and the last installment will review the Transitional and unilateral presentations.
Each installment will review some rehab concepts around exercises to improve self-bracing, and what to avoid for each type. The rehab is based on the recent pilot study I have collaborated on with EIT Sport Science Department, Hawkes Bay.
Joint Anatomy
The morphology of the sacroiliac (SI) joint varies considerably with age, among individuals, and even from side to side in the same individual.
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It represents the largest paraxial joint, with a surface area of more than 17 cm 2 in adults.
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The SI joint is innervated by the L5 and S1 through S4 dorsal rami nerve roots.
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The sacro-iliac joint has very few muscular motivators. This is the only joint or articulation in the human body not endowed with voluntary muscle control
The sacro-iliac joint proper has three ligaments:Anterior sacro-iliac, Posterior sacro-iliac and The Interosseous ligaments.
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The SI Joint is not your typical diarthrodial joint, it has two joint surfaces, synovial fluid and a fibrous capsule that may be absent posteriorly. The surfaces are not smooth – they are full of ridges, valleys, bone spurs and then sclerosis in later life
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Anatomical location
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SOT terminology
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Type
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Function
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The anteroinferior ventral
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Boot mechanism
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Synovial with soft fibrocartilage
Articular
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Motion Rocker, semi rotating gliding motion, primary sacral respiratory boot motion
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posterosuperior part is a fibrous joint supported by powerful ligaments.
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Weight bearing part
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Hyaline – held together with interosseous fibres
ligamentous
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Stability – weight bearing portion
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A potential source of pain is when trauma ruptures the synovial capsule and fluid leaks into the usually dry hyaline environment, and the L5 dorsal rami.
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· Though the range of motion of the SIJ is only a few degrees, the human body would not function well without it. Essential for the sacral occipital pump action for CSF
· The SIJ, which is one of the few joints parallel to the gravity line, plays a leading role in absorbing vertical loads
· Highly populated with proprioceptive cells
· The SIJ supports upper body weight and absorbs impact from the ground.
· When loaded, the SIJ absorbs load like a damper, while locking instantly and gradually moving.
· Shearing force in the SIJ is prevented by a combination of form closure and force closure
19-30% of all low back pain is attributed to SIJD. Mounting evidence on CT, MRI and scintigraphy demonstrate destructive, inflammatory, and degenerative pathology. Acute (subchondral bone edema, enthesitis, synovitis and capsulitis) and chronic (erosions, subchondral bone sclerosis, bony bridges, and fatty infiltration) suggests that the joint should be considered a potential source of low back dysfunction.
Motion and Stability
For the sake of this article I have kept the details brief on the self-bracing and compressive forces that stabilise the SI joint – if anyone is interested, I am happy to forward the article by Dontigny that goes into more details.
The Ilium does not fit compactly into or onto the sacrum, rather it is supported by cartilage, ligaments and tendons.
Stability is gained through a mechanism of self-bracing. The extremely dense structure of the SIJ stores ligamentous tension which increases and draws the sacroiliac surfaces tightly together with movement. Self-bracing allows greater ligamentous tension for the storage and release of energy and serves to balance forces of gravity, weight-loading, inertia, rotation, and acceleration and deceleration. A very complex tensegrity model.
The sacro-iliac weight bearing articulation functions not as a segregated unit of structure, but as a unit dependent upon the femoral heads, necks and the shaft angles and alignment, plus the lower three lumbar vertebrae and their ligaments, tendons, muscles and dural attachments via the anterior broad ligament.
There are several myofascial structures that influence movement and stability, the most notable of which are the latissimus dorsi via the thoracolumbar fascia, the gluteus maximus, and the piriformis – remember this when we get to rehab.
Failure of the force couple due to trauma, chemical/hormonal changes in ligament tension, emotional stress in the ligaments causes failure of the transverse axis of rotation of the sacroiliac joint and failure of the self-bracing mechanism. The resultant dysfunction may range from slight to severe, from minor ligamentous sprains to major sprains, muscle separations, and rents in the joint capsule.
These rents may leak synovial fluid to the fifth lumbar nerve root, the lumbosacral plexus, and other tissues; and the resulting lesion may mimic disc dysfunction or create the impression of a multifactorial etiology.
Histologic analysis of the sacroiliac joint has verified the presence of nerve fibers within the joint capsule and adjoining ligaments. Samples of capsular ligamentous tissue from the ventral aspect of the SIJ were obtained from macroscopically normal but chronically painful SI joints. The tissue was examined microscopically and revealed both nerve fascicles and individual axons (21,27). The nerve fascicle contained both myelinated and unmyelinated nerve fibers, two morphotypes of paciniform-encapsulated mechanoreceptors, and a single nonpaciniform mechanoreceptor (21,27-30). This would strongly suggest that both pain and proprioception are transmitted from the SIJ (17,21,26,28-30)
Morphology
Anatomically there is considerable variety in the mechanical structure of the sacro-iliac articulation. Consistent viewing of A-P radiographs of the sacro-iliac joint shows a great number of variations. Anatomical variance from side to side is more the rule than the exception. However, there are generally five types of articulations, with varying degrees of strength and stability.
- 1. The normal inverted S joint
- 2. The straight or slip joint
- 3. The Tubercle
- 4. The C shaped joint
- 5. The transitional segment
1. Normal Inverted ‘S shaped’ Sacro-iliac Joint
The first type is slightly curved with an inverted “S” formation at the lower portion. This creates a shelving effect with a significant amount of stability. When viewed on the A-P radiograph, this joint appears to be about 2mm wide. The normal joint has no sclerosing along its margins and no lipping or spurring along the inferior of superior margin.
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Clinical Consideration: This is considered the most stable and least troublesome type. Therefore a patient prognosis is good with little ongoing issues or repercussions. Remember that trauma causing a sprain of the ligaments is still graded I-IV. And follows similar etiology for an ankle sprain.
o When sclerosing at the margins is seen on X-ray and as the joint gap is 3mm or more the joint is noted to be more unstable clinically. This is an adaptation due to the inability of the interosseous ligaments to restrict the sacro-iliac articulation to its normal range of motion. Often a chronic Category II presentation, chronic SI joint sprain – presenting as acute on chronic. So patient communication should include the possibility of reoccurrences if not managed properly.
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Rehab/Home care: Aim is always to restore normal thoracolumbar fasica compressive forces and ligamentous tension and avoid aggravation.
· Walking with arms swinging, on flat surfaces for 15-20 min 1-2 times a day is ideal. This activates tension in the posterior chain, sacrotuberous ligaments and thoracolumbar fascia with arms moving.
· Bird dog – on all fours lifting opposite arms and legs, increases thoracolumbar fasical action.
· Hip Bridges – glut, lower core and psoas activation. Include pelvic floor activation for added stability.
· As always, these basic levels should be progressed i.e. walking up and down hills, bird dog with a weight in one hand, hip bridges with feet on a BOSU or unstable surface.
· These shapes have no contraindications to any exercise type within ability, pain and other patient issues.
2. C-Shaped Sacro-Iliac Joint
The most unstable of all, particularly when seen bilaterally, is the “C” shaped sacro-iliac articulation. This shape allows a mechanical wobbling type motion of the sacrum around the central axis of the second sacral tubercle. Think of a loose wheel on a bike. This side-to-side wobble increases if the joint space becomes widened due to repeated trauma or stretching of the ilio-lumbar ligaments. This in turn compromises the reciprocal tension stability and self-bracing ability of the pelvis.
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Clinical consideration: These joints are easy to spot - while walking a person’s legs tend to swing around and the bottom has more of a ‘hippo’ wobble. Tend to squat unevenly if unilateral, generally don’t like standard squats - want to move their legs out. Don’t like wearing the SI belt for long periods of time.
o Respond well to SOT Blocking, difficult to manually adjust due to angles of SI joint.
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Rehab: Start with simple wall sits aiming for a minute,
o Bird Dog: need to put a weight or a book on their sacrum/low back for external feedback so they don’t roll their pelvis when lifting the leg –
o Squats: best with wide squats, sumo style
o Hip Bridges safe but make sure they are squeezing gluts together on the way up
o Bear walks – again good to do but put weight on low back so the form is corrected, and lower core must work more intensely
o Will take 3 months to get more stable.
Sacroiliac joint morphology may not be something routinely look at with x-rays, however by looking at the different shapes you can tailor your adjustments, rehab, advice and expectations with more favourable outcomes.
Like our SOT NZ facebook page to keep up with the latest and you will get reminded when part 2 is posted, or visit our website at www.soto.nz
In 2020 we are running the first ever South Island Basic SOT series in Christchurch, we would love to see you there.
Thank you and any questions please email secretary@soto.nz
References:
SOT Introduction to Categories, Feb 2017, SOTO International and SOTO Australia
Topographic MRI evaluation of the sacroiliac joints in patients with axial spondyloarthritis☆Laís Uyeda Aivazogloua et al
The Sacroiliac Joint: Anatomy, Physiology and Clinical Significance,Stacy L. Forst, PA-C, Michael T. Wheeler, DO, Joseph D. Fortin, DO, and Joel A. Vilensky, PhD Pain Physician. 2006;9:61-68, ISSN 1533-3159
Critical Analysis of the sequence and extent of the result of the pathological failure of self bracing of the sacroiliac joint.; Richard L Dontigny, PT Havre, Montana, (JMMT 1999; 7: 173-181).